The present invention relates to a method of manufacturing a surface acoustic wave (SAW) device, such as a SAW filter.
A conventional method of manufacturing a surface acoustic wave device (SAW device) is shown in FIG. 5.
A metal layer which comprises Alxe2x80x94Cu (aluminum-copper alloys) is formed on a piezoelectric substrate 51 made of LiTaO3. Then, the metal layer is patterned using a conventional photo-lithography etching method to form an interdigital electrode 52, as shown in FIG. 5(A).
An oxide layer 53 is formed on the substrate 51. Then, a part of the oxide layer 53, which corresponds to a pad region where a bonding pad will be formed later, is opened using the conventional photo-lithography etching method, as shown in FIG. 5(B).
Then, a resist layer 54 is formed on and above the substrate 51. The resist layer 54 is opened in the pad region such that a side surface thereof is inversely tapered, as shown in FIG. 5(C).
A pad electrode layer 55 is formed on and above the substrate 51, as shown in FIG. 5(D). The pad electrode layer 55 is comprised of two layers, with the lower layer thereof being Cr (chromium) or Ti (titanium) and the upper layer thereof being Au (gold).
Then, the resist layer 54 is removed by acetone and a bonding pad 56 is formed using a conventional lift off method, as shown in FIG. 5(E).
However, using the lift off method, it is initially difficult to obtain regularly shaped bonding pads. Further, a material of the pad electrode layer which does not dissolve in the acetone can sometime attach to the substrate.
To avoid such problems, one might consider forming the bonding pad using a conventional photo-lithography etching process. However, the oxide layer on the interdegital electrode is extremely thin, which is a characteristic of the SAW device. Therefore, if the bonding pad were etched using the conventional photo-lithography etching process, the interdigital electrode under the oxide layer would likely be etched as well. This would adversely change the characteristics of the SAW device.
An object of the present invention is to provide a method of manufacturing a surface acoustic wave (SAW) device in which a bonding pad may be formed using a photo-lithography etching process without changing the characteristics of the SAW device.
To achieve the above and other objects, an interdigital electrode of a SAW device according to the invention is protected by a protective layer during a photo-lithography etching process which is applied to a bonding pad.
According to the present invention, as the bonding pad can be formed using a photo-lithography etching process, it is possible to obtain regularly shaped bonding pads without damaging the characteristics of the SAW device